This invention relates to automatic welding and more specifically to automatic welding using a charge injection device forming part of the closed circuit television camera that is used for guiding a welding torch along a joint.
Heretofore, many different methods have been developed to provide automatic precision welding. When welding relatively large articles together such as, for example, tanks, ship hulls, etc., a type of automatic control utilizing a track and carriage is normally used. This requires precision placement of the track relative to the seam that is to be welded. One type such device is disclosed in U.S. Pat. No. 3,229,883.
As more sophisticated needs for welding have developed such as welding space vehicles and the like, it is important that the quality of the weld be extremely high so as to pass extensive tests and examination. From the tests provided on welds, flaws often show up which require re-welding of the seams and sometimes discarding of the material that is to be welded.
In an attempt to overcome these problems, there has been disclosed in U.S. Pat. No. 3,532,807 a method for automatically welding a workpiece by using a closed circuit television as a guidance system. With the television camera viewing the workpiece, the lines of scan of the television are arranged parallel to the joint to be welded so that with the proper arrangement of lights, the brightest light received by the television comes from the joint to be welded. With a blanking circuit to eliminate errors caused by light reflected from scratches and rough spots, all that is left is the television signal voltage generated from the bright weld joint along the single line of scan. As the weld torch is moved along the surface, corrections are made by counting the position of the line of scan containing reflections from the weld point and converting a change in position of reflection to an analog signal. A servo motor is driven by the analog voltage to correct variations in position of the weld torch.
One problem with such a method is that it requires the light source to illuminate the weld joint to be located very close and at a very disadvantageous position to the weld joint. It also requires special weld joint preparation to accommodate the seam tracking. More specifically, the weld joint was required to be chamfered to assure that the light striking the chamfer from the light source was reflected into the CCTV camera.
Another disadvantage is that the light source had to be maintained at a specific height above the workpiece in order to properly operate the tracking system. Still another disadvantage of the prior art system is that if the two pieces of metal to be welded together at the joint are offset to each other, that would adversely effect the welding operation due to the manner in which the light is reflected from the chamfered surface.
Accordingly, it is an object of the present invention to provide a reliable, fully digital automatic closed circuit television seam tracking control system for accurately guiding a weld torch along a joint to be welded.
Another important object of the present invention is to provide an apparatus for welding joints that is easily adaptable to a variety of weld process systems.
Still another important object of the present invention is to provide an automatic guidance system for a welding torch that does not require extensive workpiece preparation.
A further important object of the present invention is to provide a guidance system for a welding torch that utilizes a TV camera and a light source wherein the illumination from the light source is not critical as to alignment, brightness and proximity to the workpiece.
Still another important object of the present invention is to provide a guidance system for an automatic welding apparatus wherein errors due to workpiece scratches, loss of signal, extraneous light reflection, workpiece offset or workpiece hold-down fixturing is eliminated or minimized.